1. Field of the Invention
This invention relates generally to an apparatus for remote monitoring of a rotary valve position. More specifically, this invention relates to an improved construction of a rotary valve position indicator.
2. Description of the Background
Remote monitoring and control of flow systems having numerous valves is often provided by computers using specialized software. An electrical valve position indicator may be used with each monitored valve to provide a signal to the system control computer. Generally, the signal provided by a valve position indicator is indicative of a status condition of the particular valve, such as whether the valve is fully open, fully closed, partially open, and so forth.
Electrical devices that have been used in the past to perform this function have had numerous problems. For instance, the switch indicators available to monitor valves must be sturdy and so are often supplied in large, bulky housings that have numerous crevices, dead-end holes, and other irregularities. Such devices often tend to collect dirt in the cracks and crevices and so are not suitable for operation in food processing environments, such as breweries, that require a high degree of cleanliness.
The electrical switches used in these bulky indicators often have "bounce" problems that may produce false signals in a control system. Furthermore, the switch contacts in such devices are often affected by moisture or other factors so that even if the contacts close properly, they may still have too much contact resistance to allow proper electrical signal flow. This may be especially true for relatively low amperage signals associated with solid state automation control systems. Such problems may cause system operation errors by producing false or intermittently faulty signals.
Even sealed contacts may eventually develop contact resistance problems. Due to the weather-proof or explosion-proof housings of electrical contact boxes, it is difficult and time-consuming for an operator to check whether a fault condition is the result of the contacts being closed but not conducting, or whether the contacts failed to close altogether, or whether the electrical problem lies somewhere in the cabling or interconnections. Once the housing is removed, the contact box is no longer explosion-proof, and activation of a switch during checking or maintenance could ignite flammable or explosive vapors.
As well, electrical connections to the housings are often difficult and time-consuming to complete because they require disassembly of covers or lids from their respective bases. If the cover or lid is not properly reassembled, then leakage eventually occurs that may cause system problems. In some cases, electrical cable conduits go through various ambient temperature conditions that cause them to gradually fill with condensation that eventually makes its way back into otherwise weatherproof switch housings. Weather-proof switches may not be adequately sealed when the switch housings are flushed with fluids or submersed as could happen when a plant is being cleaned.
Furthermore, heavy and bulky valve position indicators, though sturdy, may be easily broken or damaged if dropped, or due to corrosion, or due to leakage in the switch indicator housings. The mounting of the switch indicator devices to the valve actuator assemblies is often cumbersome and difficult because it requires threading and tightening of numerous small screws or nuts. The metallic construction of many switches eventually results in corrosion that causes the switch installation to physically seize up, weaken or come loose, leak, or otherwise operate in an undesirable manner.
Heavy valve switch boxes are expensive and require considerable ongoing maintenance. Because the switch indicators are large, bulky, and clumsy, they are difficult to manufacture and have tended in the past to spawn many different nonstandardized brands that may have to be used in a single system. Switch packages are typically cumbersome in that two separate packages must be used to provide an open position switch and a closed position switch.
The power supplied to some valve position indicators, especially those that use inductive or capacitive proximity detectors, requires precise voltage specifications and cannot be used without modification for both alternating and direct current power. Power fluctuations may cause false signals to be produced in such valve position indicators to thereby deleteriously affect the computer control system.
As well, valve position indicators are typically sensitive to load variations. For instance, a valve position indicator designed for use with an inductive load may cause system problems when used with a solid state load. A solid state valve position indicator that is required to even momentarily switch a load outside its tolerances will often fail.
Another problem with prior art position indicators concerns mechanical adjustment provisions for selecting a desired rotary angle of the valve at which a switch provides an open or close signal. In some systems, the rotary angle at which a switch opens or closes is not critical, so long as it is consistent, because the angle(s) may be entered into a control program that accounts for this factor. In other systems, it is necessary to mechanically adjust switch activation to occur at the desired degree of rotation of the valve. Adjustment means of prior art devices typically have problems relating to (1) mechanical wear that causes gradual changes in switch position activation, (2) gearing or splining problems that allow only relatively course adjustments, (3) exposed switches during adjustments that could ignite flammable gases, (4) poorly marked adjustment assemblies that lend themselves to adjustment errors, and (5) problems related to prior art position indicator device shortcomings discussed hereinbefore.
Consequently, there remains the need for an improved rotary valve indicator that offers dependable operation at reduced levels of capital investment, is compact, is easily cleaned, handles small power signals without contact bounce problems, operates reliably even with wide power fluctuations and different types of loads, provides hermetically sealed switch contacts, is rugged and reliable, is submersible and explosion-proof, is easily mounted, requires little maintenance, is easily and safely adjustable, and is of such low cost that it can be thrown away if failure occurs. Those skilled in the art have long sought and will appreciate the present invention, which provides solutions to these and other problems.